1. Field of the Invention
The present invention relates to a technique capable of lessening bleeding which occurs upon the formation of color images with inks and providing images high in water fastness. In particular, it relates to an image-forming process and an apparatus making good use of an ink-jet system, and a liquid composition and an ink set, which are suitable for use in such process and apparatus.
2. Related Background Art
An ink-jet recording method is a system in which recording is conducted by flying out droplets of an ink to apply them to a recording medium such as paper. In particular, according to the methods disclosed in Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914, in which an electrothermal converter is used as an ejection-energy supply means to apply thermal energy to an ink so as to generate bubbles, thereby ejecting droplets of the ink, the formation of a high-density multi-orifice in a recording head can be realized with ease, and high-resolution and high-quality images can be recorded at high speed.
However, the conventional inks used in ink-jet recording generally comprise, as a principal component, water, and include additionally a water-soluble high boiling solvent such as glycol for the purpose of preventing drying and clogging, and the like. When such an ink has been used to conduct recording on plain paper, there have been encountered disadvantages that fixing ability cannot be sufficiently achieved, and image irregularity occurs, which appears to be attributed to the uneven distribution of the filler and size on the surface of the recording paper. In particular, when color images are intended to form, plural inks of different colors are overlapped one after another before they are fixed to paper. Therefore, color bleeding and uneven color mixing have occurred at portions of boundaries between images of different colors (this phenomenon will hereinafter be referred to as xe2x80x9cbleedingxe2x80x9d simply), resulting in a failure to obtain satisfactory images.
As a means for enhancing fixing ability of inks, Japanese Patent Application Laid-Open No. 55-65269 discloses the addition of a compound capable of enhancing penetrability, such as a surfactant, into the inks. Besides, Japanese Patent Application Laid-Open No. 55-66976 discloses the use of inks comprising, as a principal component, a volatile solvent. However, the former method has involved a disadvantage that although the penetrability of the inks into recording paper is improved, and so the fixing ability is improved and bleeding can be prevented to some extent, the image density and the saturation of the resulting image are lowered because coloring materials penetrate deeply into the recording paper together with the inks. In addition, the inks have also involved a problem that they spread in lateral directions, resulting in reduction of edge sharpness and resolution. On the other hand, the latter method is liable to cause clogging due to the evaporation of the solvent in a nozzle of a recording head in addition to the above-described disadvantages. Such methods have hence not been preferred.
In order to improve the above-described problems, further, there have been disclosed methods of applying a liquid, which can make the quality of images better, to a recording medium prior to the jetting of a recording ink.
For example, Japanese Patent Application Laid-Open No. 63-60783 discloses a method in which a liquid containing a basic polymer is applied to a recording medium, and recording is then conducted with inks containing an anionic dye. Japanese Patent Application Laid-Open No. 63-22681 discloses a recording method in which the first liquid containing a reactive chemical species and the second liquid containing a compound reacting with the reactive chemical species are mixed on a recording medium. Japanese Patent Application Laid-Open No. 63-299971 discloses a method in which a liquid containing an organic compound having two or more cationic groups per molecule is applied to a recording medium, and recording is then conducted with inks containing an anionic dye. Japanese Patent Application Laid-Open No. 64-9279 discloses a method in which an acidic liquid containing succinic acid or the like is applied to a recording medium, and recording is then conducted with inks containing an anionic dye.
Further, Japanese Patent Application Laid-Open Nos. 64-63185 and 64-69381 disclose a method of applying a liquid, which insolubilizes dyes, to a recording medium prior to recording.
However, all these methods intend to prevent bleeding of images or improve the water fastness of images owing to the deposition of the dyes themselves in the inks. Therefore, these methods are still insufficient in the effect to prevent the above-described bleeding between inks of different colors, and moreover poor in coverability of the inks on pulp fibers in the recording paper because the dyes deposited tend to distribute unevenly on the recording paper, resulting in reduction of evenness of images.
With the foregoing circumstances in view, the present invention has been completed with a view toward satisfying the following five requirements for ink-jet recording on plain paper:
(1) being able to provide images excellent in quality of characters while retaining good fixing ability;
(2) being able to achieve sufficient image density and provide solid images high in evenness; and in particular, upon formation of color images on plain paper;
(3) being able to prevent bleeding;
(4) being excellent in color reproductivity and being able to provide high-fine images; and
(5) being able to achieve perfect water fastness of recorded images.
The above object can be achieved by the present invention described below.
In the first aspect of the present invention, there is provided a liquid composition comprising a cationic substance, wherein the liquid composition contains in combination a cationic substance and a nonionic polymeric substance.
In the second aspect of the present invention, there is provided a liquid composition comprising a cationic substance, wherein the liquid composition contains in combination a cationic oligomer having a molecular weight distribution in which a peak exists in a molecular weight region, and a nonionic polymeric substance.
In the third aspect of the present invention, there is provided a liquid composition comprising a cationic substance, wherein the cationic substance has a molecular weight distribution in which at least one peak exists in two molecular weight regions.
In the fourth aspect of the present invention, there is provided an ink set comprising in combination one of the above-described liquid compositions and at least one of yellow, magenta, cyan, black, red, blue and green inks.
In the fifth aspect of the present invention, there is provided an ink set comprising in combination one of the above-described liquid compositions and three inks of yellow, magenta and cyan colors.
In the sixth aspect of the present invention, there is provided an ink set comprising in combination one of the above-described liquid compositions and four inks of yellow, magenta, cyan and black colors.
According to the present invention, the above inks may contain an anionic compound, and the anionic compound may be a polymeric substance having a molecular weight of at least 5,000, or a surfactant.
In the seventh aspect of the present invention, there is provided a process of forming an image, which comprises the steps of (A) applying one of the above-described liquid compositions to at least an image-forming region of a recording medium and (B) applying an ink comprising an anionic compound to the recording medium by an ink-jet system.
In the eighth aspect of the present invention, there is provided an image forming apparatus comprising one of the above-described ink sets and an ink-jet means.
In the ninth aspect of the present invention, there is provided an image forming apparatus comprising the first recording unit equipped with a container part containing one of the above-described liquid compositions and an ejection means therefor, and the second recording unit equipped with container parts separately containing inks comprising an anionic compound and ejection means therefor.